PROJECT SUMMARY/ABSTRACT The central goal of this project is to develop new sulfur fluoride exchange (SuFEx) reactions to construct small-molecule libraries containing the SVI-F motif and to explore their in vitro and in vivo functions. SuFEx is a new family of click chemistry transformations for generating diverse chemical structures bearing the SVI-F motif, such as -OSO2F (fluorosulfate) and -SO2F (sulfonyl fluoride). In the last funding period, we established three versatile SulfurVI connectors: sulfuryl fluoride (SO2F2), ethenesulfonyl fluoride (ESF) and thionyl tetrafluoride (SOF4), among which SO2F2 selectively reacts with the ? OH group of phenols to form aryl fluorosulfates. Based on this transformation, we invented extremely fast fluoride exchange reactions to introduce the fluorine-18 isotope into biologically active small-molecule radiotracers for positron emission tomography. By screening aryl fluorosulfate-based libraries, we discovered small-molecule covalent modifiers for Intracellular Lipid Binding Protein(s) and a platform for the late-stage drug functionalization. Based on these discoveries, in the next funding period, we will develop new transformations to expand the SuFEx transformation repertory (Aim 1). Using these new synthetic strategies and our established SuFEx tools, we will design and synthesize new SVI-18F agents based on amine-containing probes for positron emission tomography (Aim 2). Finally, using SuFEx chemistry, we will prepare small-molecule libraries and screen them to identify new antibiotics candidates and anti-cancer compounds (Aim 3).